1. Field of The Invention
The present invention relates generally to signal measurement systems and, more particularly, to graphically manipulating display elements in a signal measurement system.
2. Related Art
Conventional signal measurement systems such as digital oscilloscopes sample, record and display time-varying analog signals. Samples of an input signal are taken and quantized, and the resultant digital representations are stored in a waveform memory under the control of a sampling clock. The acquired data may subsequently be read out as locations in memory are sequentially addressed by a clock signal to provide digital data which can be converted to a time-varying output signal for a waveform display. The sampling clock may be operated at one of several selectable rates depending upon the frequency content of the input signal. The selection of the portion of the analog input signal which is sampled and stored is determined by appropriate triggering circuitry to enable the operator to display the desired portion of the waveform.
There are many types of display elements which can be presented in signal measurement systems in general and test and measurement instruments in particular. For example, in addition to the waveforms representing the signals currently received at the channel inputs, waveforms referred to as function waveforms may also be displayed. Function waveforms are waveforms created by processing the signal waveforms. Such processing may include, for example, performing arithmetic manipulations or combining multiple input signal waveforms in some predetermined manner. The resulting waveforms are placed in a display memory for subsequent retrieval and display. In addition, memory waveforms may also be displayed. Memory waveforms are waveforms which have been stored in memory for later display. In addition to the above waveforms, other display elements such as marker indicators, trigger level indicators, etc. are typically displayed.
Conventional signal measurement systems typically provide a display grid on which the display elements are presented. The display grid divides the coordinate axes into a series of divisions. Waveforms are displayed on the display grid and are scaled vertically and horizontally to facilitate analysis. Typically, the horizontal scale represents sweep speed and is in units of seconds per division, while the vertical scale represents signal amplitude and is in volts per division. The center of the horizontal axis represents the delay or horizontal position of the displayed waveform and is referred herein to as horizontal offset. The center of the vertical axis represents the voltage offset of the displayed waveform and is referred to as vertical offset.
Successful utilization of the signal measurement system requires the ability to adjust the placement of waveforms and other display elements on the display grid. In addition to adjusting the relative sizes of the displayed waveforms, these manipulations typically include adjustments along the two coordinate axes to adjust the vertical and horizontal offsets of a given display element. Conventional signal measurement systems typically have numerous dials and knobs to manipulate the many display elements which may be simultaneously visible on the waveform display.
In some conventional signal measurement systems the placement operations are performed through the use of one or more knobs and/or soft keys. Typically, to adjust a display element, the display element must first be selected using a soft key. Then, the proper knob or control button on a front panel keyboard must be manipulated to achieve the desired position adjustment. In other conventional signal measurement systems, display element manipulation control is provided through a numeric entry on a keypad.
There are many drawbacks to these conventional approaches. One drawback, for example, is that the user must understand the relationship between multiple separate control inputs. Similarly, when there are numeric inputs the user must understand the relationship between the numeric value associated with the control input and the associated actual position of the display element on the display. This is often not the case, causing the user to make multiple attempts to place a selected display element in a desired location.
In addition, due to the limited space on a typical front panel keyboard, conventional signal measurement systems typically assign multiple functions to each control knob or implement a complex hierarchy of soft keys. This results in a complicated display panel which is often difficult to learn and use efficiently. Moreover, the location of a desired function is not always intuitively associated with a higher level soft key and is therefore often difficult to locate.
What is needed, therefore, is an intuitive and simple technique for manipulating display elements in a signal measurement system that is fast and efficient to use and does not require a large number of control inputs. If possible, the technique should not require interpretation or conversion of numeric inputs by the user.